DESCRIPTION This proposal seeks to determine the mechanism of C-inactivation associated with voltage-gated K channels in T-lymphocytes. The first aim of the project is to test the hypothesis that interactions among the subunits of the tetrameric channel responsible for inactivation is cooperative. This hypothesis will be evaluated from changes in the time course of inactivation in heterologous expressed heteromultimeric channels assembled from wild-type and mutant subunits with different defined stoichiometries. Best fits of the data to mathematical models will be used to distinguish between different alternatives. The second aim of the study seeks to determine which regions of the subunits participate in the inactivation. Of particular focus is the role of the S1-S2 loop. Molecular biology techniques will be used express channels in which this region has been modified. Mathematical modeling of the expressed current and construction of free energy profiles for transitions between conformational states will lead to a description of a role for this region in C-inactivation.